/*
 * Copyright 2002-2007 Network Engine for Objects in Lund AB [neotechnology.com]
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 * 
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.neo4j.impl.persistence;

/**
 * The IdGenerator is responsible for generating unique ids for entities in
 * the Neo. The IdGenerator is configured via the {@link IdGeneratorModule}.
 * <P>
 * The IdGenerator must be loaded after its designated
 * {@link IdGeneratorModule#setPersistenceSource persistence source} during
 * startup.
 * <P>
 */
public class IdGenerator
{
	// -- Singleton stuff
	private static final IdGenerator instance = new IdGenerator();
	private IdGenerator() {}
	
	/**
	 * Singleton accessor.
	 * @return the singleton id generator
	 */
	public static IdGenerator getGenerator() { return instance; }
	
	
	// -- Attributes
	
	// the persistence source used to store the HIGH keys
	private PersistenceSource persistenceSource		= null;
	
	/**
	 * Returns the next unique ID for the entity type represented by
	 * <CODE>clazz</CODE>.
	 * @return the next ID for <CODE>clazz</CODE>'s entity type
	 * @throws IdGenerationFailedException if <CODE>clazz</CODE> is not
	 * a registered entity type or if communication with persistent
	 * storage failed
	 */
	public int nextId( Class<?> clazz )
	{
		return getPersistenceSource().nextId( clazz );
	}
	
	public int getHighestPossibleIdInUse( Class<?> clazz )
	{
		return getPersistenceSource().getHighestPossibleIdInUse( clazz );
	}
	
	public int getNumberOfIdsInUse( Class<?> clazz )
	{
		return getPersistenceSource().getNumberOfIdsInUse( clazz );
	}
	
	
	// -- Configuration and attribute accessors
	
	/**
	 * Configures the IdGenerator. <B>WARNING</B>: This method should
	 * only be invoked once from {@link IdGeneratorModule#start}.
	 * @param source the persistence source used for id generation
	 */
	void configure( PersistenceSource source )
	{
		// Save connectivity
		this.persistenceSource = source;
	}
	
	// Accesor for persistence source
	private PersistenceSource getPersistenceSource()
	{
		return this.persistenceSource;
	}
}
